The ECJ said employers did not have to justify, on a case-by-case basis, their pay structures based on the length of service, unless a worker could provide evidence to raise serious doubts about the process.

The court rejected a claim by Bernadette Cadman, who had said her employer, the Health and Safety Executive (HSE), unjustifiably paid her male colleagues on the same grade more only because they had worked more years.

Cadman argued that length of service and seniority often depended on domestic circumstances such as pregnancy and maternal leave and that employers must provide special justification for paying men more than women when they hold the same post.

But the ECJ said in its ruling: “Recourse to the criterion of the length of service is appropriate to attain the legitimate objective of rewarding experience acquired which enables the worker to perform his duties better.

“There is no need to show that an individual worker has acquired experience during the relevant period which has enabled him to perform his duties better.”

Cadman sued the HSE in 2001 when she discovered she was earning up to £9,000 a year less than male workers in the same post.

A UK employment tribunal initially ruled in her favour, but, on appeal, the case was referred to the ECJ which interprets pan-EU legislation.